Polysiphonia Lanosa Research Articles

Cardioprotective potential of Irish macroalgae: generation of glycine betaine and dimethylsulfoniopropionate containing extracts by accelerated solvent extraction.

Accelerated solvent extraction (ASE®) was used to generate 18 macroalgal extracts from Irish seaweeds. The glycine betaine and dimethylsulfoniopriopionate content of the generated ASE® extracts were estimated using (1)H-NMR and confirmed for selected extracts using ultra performance liquid chromatography and mass spectrometry. Dimethylsulfoniopriopionate was only identified in the ASE® extract generated from Codium fragile ISCG0029. Glycine betaine was identified in the ASE® extract generated from Ulva intestinalis ISCG0356 using (1)H-NMR. Mass spectrometry analysis found that the seaweed species Cytoseira nodicaulis ISCG0070, Cytoseira tamariscofolia ISCG0283, and Polysiphonia lanosa ISCG0462 also had a glycine betaine content that ranged from 1.39 ng/ml to 105.11 ng/ml. Generated ASE® macroalgal extracts have potential for use as functional food ingredients in food products.

A comprehensive study of metal distribution in three main classes of seaweed

This paper provides one of the most comprehensive studies of metal distributions in three main macroalgae species. In this novel study, levels of total, intracellular and surface bound Pb, Zn, As, Cd, Co, Cr, Cu, Mn and Ni associated with Polysiphonia lanosa (L) Tandy, Ascophyllum nodosum (L) Le Jolis, Fucus vesiculosus (L) and Ulva sp. were determined. Additionally, water and sediment metal levels were analysed to gain an insight into the relative uptake efficiencies of different macroalgal species. Samples were collected from a clean site in Fethard-on-Sea, Wexford, Ireland (52°11′53.68′N, 6°49′34.64′W), in May 2008.Results demonstrated that total, intracellular and surface bound metal levels varied according to metal and seaweed species, with the highest proportion of metals found to be intracellular. Inhibition of Mn uptake by Zn was indicated for P. lanosa. Furthermore, P. lanosa had enhanced bioaccumulation ability, with the highest Concentration Factor reported of any seaweed to date.

Properties of polysaccharides in several seaweeds from Atlantic Canada and their potential anti-influenza viral activities

To explore the polysaccharides from selected seaweeds of Atlantic Canada and to evaluate their potential anti-influenza virus activities, polysaccharides were isolated from several Atlantic Canadian seaweeds, including three red algae (Polysiphonia lanosa, Furcellaria lumbricalis, and Palmaria palmata), two brown algae (Ascophyllum nodosum and Fucus vesiculosus), and one green alga (Ulva lactuca) by sequential extraction with cold water, hot water, and alkali solutions. These polysaccharides were analyzed for monosaccharide composition and other general chemical properties, and they were evaluated for anti-influenza virus activities. Total sugar contents in these polysaccharides ranged from 15.4% (in U. lactuca) to 91.4% (in F. lumbricalis); sulfation level was as high as 17.6% in a polysaccharide from U. lactuca, whereas it could not be detected in an alikali-extract from P. palmaria. For polysaccharides from red seaweeds, the main sugar units were sulfated galactans (agar or carrageenan) for P. lanosa, F. lumbricalis, and xylans for P. palmata. In brown seaweeds, the polysaccharides largely contained sulfated fucans, whereas the polysaccharides in green seaweed were mainly composed of heteroglycuronans. Screening for antiviral activity against influenza A/PR/8/34 (H1N1) virus revealed that brown algal polysaccharides were particularly effective. Seaweeds from Atlantic Canada are a good source of marine polysaccharides with potential antiviral properties.

Marginal populations under pressure: spatial and temporal heterogeneity of Ascophyllum nodosum and associated assemblages affected by human trampling in Portugal

Anthropogenic disturbances are major threats to coastal biodiversity and may exert drastic effects on natural populations occurring at the borders of the geographical distribution of species, which are thus already experiencing sub-optimal environmental conditions. In this paper, we examined the effects of experimental intensities of human trampling on temporal and spa - tial variance of the brown seaweed Ascophyllum nodosum and associated organisms in north Por tugal. This is the southernmost population of A. nodosum in Europe and shows morphological and demographic traits that are different from those of populations from more central locations within its range of distribution. Results indicated that high trampling intensity reduced the small- scale spatial heterogeneity in the abundance of A. nodosum, whose cover was stabilized around relatively low values, and of the associated red algae Polysiphonia lanosa and Rhodothamniella floridula; however, it increased the spatial variance of limpets and green foliose macroalgae of the genus Ulva. Idiosyncratic responses in temporal patterns were also documented, with high tram- pling intensity causing relatively larger fluctuations in the structure of whole A. nodosum associ- ated assemblages and in the abundance of Ulva spp., and smaller fluctuations in the cover of Fucus vesiculosus. The present findings are key to predicting the relatively unstudied responses of coastal populations of A. nodosum to increasing anthropogenic disturbance and have important implications for the management and conservation of the examined population, which represents a relevant component of the biodiversity of European rocky shores.

Research note: Field evaluation of epiphyte recruitment (Vertebrata lanosa, Rhodophyta) in different microsite types on host fronds (Ascophyllum nodosum, Phaeophyceae)

SUMMARYThe seaweed Ascophyllum nodosum (Phaeophyceae, Fucales) often forms extensive beds in wave‐sheltered, rocky intertidal habitats on northern Atlantic shores. Since this alga is an ecosystem engineer that influences benthic biodiversity, it is important to understand the factors that regulate its performance. Epiphytism is known to affect the performance of macroalgal hosts. In this study, we investigated the effects of surface irregularities on A. nodosum fronds (wounds, branch axils, and lateral pits resulting from receptacle shedding) on the recruitment rate of its obligate epiphyte Vertebrata lanosa (=Polysiphonia lanosa, Rhodophyta, Ceramiales). For this purpose, we performed a field experiment in Nova Scotia, Canada. In June–July 2007, we created wounds on the surface of host fronds that mimicked the wounds that result from invertebrate grazing. At that time, we also mapped the position of epiphyte‐free lateral pits and branch axils on host fronds. In October 2007, after the reproductive season for V. lanosa, the percentage of microsites colonized by this epiphyte was statistically similar for wounds and lateral pits, but significantly lower for branch axils, although by a small difference (mean recruitment rates ranged between 37 and 50%). Since V. lanosa is known not to colonize smooth frond surfaces, our study suggests that the degree of epiphyte load on A. nodosum beds should largely be affected by the overall amount of surface irregularities, with little influence of the relative availability of each microsite type.

Competitive Sorption of Antimony with Zinc, Nickel, and Aluminum in a Seaweed Based Fixed‐bed Sorption Column

AbstractThe removal of heavy metals such as Ni(II), Zn(II), Al(III), and Sb(III) from aqueous metal solutions was investigated using novel, cost effective, seaweed derived sorbents. Studies with a laboratory scale fixed‐bed sorption column, using a seaweed waste material (referred to as waste Ascophyllum product (WAP)) from the processing of Ascophyllum nodosum as biosorbent, demonstrated high removal efficiencies (RE) for a variety of heavy metals including Ni(II), Zn(II) and Al(III), with 90, 90 and 74% RE achieved from initial 10 mg/L metal solutions, respectively. The presence of Sb(III) in multi component metal solutions suppressed the removal of Ni(II), Zn(II) and Al(III), reducing the RE to 28, 17 and 24%, respectively. The use of Polysiphonia lanosa as a biosorbent showed a 67% RE for Sb(III), both alone and in combination with other metals. Potentiometric and conductometric titrations, X‐ray photoelectron and mid‐infrared spectroscopic analysis demonstrated that carboxyl, alcohol, sulfonate and ether groups were heavily involved in Sb(III) binding by P. lanosa. Only carboxyl and sulfonate groups were involved in Sb(III) binding by WAP. Furthermore, a greater amount of weak acidic groups (mainly carboxylic functions) were involved in Sb(III) binding by P. lanosa, compared to WAP which involved a greater concentration of strong acidic groups (mainly sulfonates).

DISTRIBUTION OF ALGAL EPIPHYTES ACROSS ENVIRONMENTAL GRADIENTS AT DIFFERENT SCALES: INTERTIDAL ELEVATION, HOST CANOPIES, AND HOST FRONDS(1).

Understanding epiphyte distribution in coastal communities is important because these organisms affect many others directly or indirectly. Yet, their distribution has been considerably less studied than that of their hosts and other primary-space holders. Identifying major sources of variation in epiphyte abundance is thus still a need. Environmental gradients help predict species distribution and are pervasive on marine shores. In this study, we test the notion that environmental gradients across intertidal elevation, throughout host canopies, and along host fronds explain a large variation in the abundance of sympatric epiphytes. Our model system was the assemblage of Ascophyllum nodosum (L.) Le Jol. and its epiphytes Vertebrata lanosa (L.) T. A. Chr. [= Polysiphonia lanosa (L.) Tandy], Elachista fucicola (Velley) Aresch., and Pylaiella littoralis (L.) Kjellm. On the coast of Nova Scotia (Canada), we found evidence of a spatial segregation among these species at almost all scales. While the red epiphyte V.lanosa was more common at high- and midintertidal elevations (peaking at midelevations) and on middle segments of host fronds, the brown epiphytes E.fucicola and P.littoralis were more common at low elevations and restricted to distal segments of host fronds. Canopy habitat affected abundance only for V.lanosa, which was more common within the host canopy than on its periphery at midelevations. Since the studied gradients are related to predictable changes in abiotic factors, the identification of likely causes behind the observed patterns was facilitated. Our study ends by proposing abiotic and biotic factors that deserve priority in the experimental testing of the forces structuring this assemblage.

ROLE OF SURFACE WOUNDS AND BROWN ALGAL EPIPHYTES IN THE COLONIZATION OF ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE) FRONDS BY VERTEBRATA LANOSA (RHODOPHYTA)(1).

Ascophyllum nodosum (L.) Le Jol. forms extensive beds in wave-sheltered, rocky intertidal habitats on the northwestern Atlantic coast. This fucoid seaweed is host to an obligate red algal epiphyte, Vertebrata lanosa (L.) T. A. Chr. [=Polysiphonia lanosa (L.) Tandy], and two facultative brown algal epiphytes, Elachista fucicola (Velley) Aresch. and Pylaiella littoralis (L.) Kjellm. Although V. lanosa can occur throughout most of the length of host fronds, it largely predominates in midfrond segments. The two brown algal epiphytes are restricted to distal segments. Through field experiments conducted in Nova Scotia, Canada, we tested the hypothesis that surface wounds are required for the colonization of distal segments of host fronds by V. lanosa. Distal tissues normally have a smooth surface because of their young age (A. nodosum fronds grow apically). By creating small wounds that mimicked grazing wounds distributed elsewhere on host fronds, we demonstrated that V. lanosa can colonize distal frond segments during the growth and reproductive season (summer and autumn). Approximately half of the artificial wounds were colonized by V. lanosa during this time. The experimental exclusion of both brown algal epiphytes from distal frond segments did not affect colonization by V. lanosa. Thus, we conclude that the absence of surface irregularities on distal segments of host fronds, specifically small wounds, is the main factor explaining the absence of V. lanosa there. We propose that further experimental work clarifying epiphyte distribution in host beds will enhance our ability to understand the functional role of epiphytes in intertidal ecosystems.

Antioxidant and cytotoxic activities of some red algae (Rhodophyta) from Brittany coasts (France)

Abstract We assessed the antioxidant activity of crude extracts from 24 rhodophyte species from Brittany coasts using three complementary methods (2,2-diphenyl-1-picryhydrazyl, reducing activity, and β-carotene-linoleic acid system). We also examined phenolic contents. Cytotoxic activities were determined with three different cancer cell lines. Four species (Aglaothamnion pseudobyssoides, Furcellaria fastigiata, Polysiphonia lanosa, and Heterosiphonia plumosa) had high antioxidant activity and high phenolic content. The extract from Brongniartella byssoides had the highest antioxidant potential, which was also found to be equivalent to the antioxidant activities of some commercial antioxidants. In the β-carotene system, extracts from Porphyra leucosticta and Porphyra purpurea had some specific antioxidant activity. Furthermore, Asparagopsis armata, B. byssoides and H. plumosa extracts had strong cytotoxic activities against Daudi and Jurkat cells.

Enhancement strategies for Cu(II), Cr(III) and Cr(VI) remediation by a variety of seaweed species

Various chemical treatments have been applied to six brown, red and green seaweed species with a view to enhancing their metal removal for Cu(II), Cr(III) and Cr(VI). Treatment with acetone resulted in the greatest enhancement for both cationic and anionic species with relatively low mass losses (15–35%), indicating its low risk to biomass operational stability. Cation binding was increased by 69%, while the total Cr removal was augmented by 15%. Cr(VI) binding was shown to be an adsorption-coupled reduction, whereby Cr(VI) was bound to the biomass surface at pH 2 and subsequently reduced to Cr(III). Acetone treatment also resulted in biomasses that were capable of converting up to 83% of Cr(VI) in solution to Cr(III). Blocking of carboxyl and amino functionalities had significant negative effects both on total Cr removal as well as percentage conversion of Cr(VI) to Cr(III). Results therefore indicated the significant role played by these moieties in metal binding to these seaweeds. Potentiometric titrations displayed agreement between the degree of esterification and the decrease in Cu(II) removal for Ulva spp. and Polysiphonia lanosa. FTIR analysis identified changes in biomass functionality and availability after chemical modification, the results of which were in agreement with metal removal studies. In conclusion, these biosorbents represent suitable candidates to replace conventional removal technologies for metal bearing wastewaters, in particular for the detoxification of hazardous Cr(VI) waste streams.

Comparative study of chromium biosorption by red, green and brown seaweed biomass

Dried biomass of the macroalgae Fucus vesiculosus and Fucus spiralis (brown), Ulva spp. (comprising Ulva linza, Ulva compressa and Ulva intestinalis) and Ulva lactuca (green), Palmaria palmata and Polysiphonia lanosa (red) were studied in terms of their chromium biosorption performance. Metal sorption was highly pH dependent with maximum Cr(III) and Cr(VI) sorption occurring at pH 4.5 and pH 2, respectively. Extended equilibrium times were required for Cr(VI) binding over Cr(III) binding (180 and 120 min, respectively) thus indicating possible disparities in binding mechanism between chromium oxidation states. The red seaweed P. palmata revealed the highest removal efficiency for both Cr(III) and Cr(VI) at low initial concentrations. However, at high initial metal concentrations F. vesiculosus had the greatest removal efficiency for Cr(III) and performed almost identically to P. lanosa in terms of Cr(VI) removal. The Langmuir Isotherm mathematically described chromium binding to the seaweeds where F. vesiculosus had the largest q max for Cr(III) sorption (1.21 mmol g −1) and P. lanosa had the largest Cr(VI) uptake (0.88 mmol g −1). P. palmata had the highest affinity for both Cr(III) and Cr(VI) binding with b values of 4.94 mM −1 and 8.64 mM −1, respectively. Fourier transform infrared analysis revealed interactions of amino, carboxyl, sulphonate and hydroxyl groups in chromium binding to Ulva spp. The remaining seaweeds showed involvement of these groups to varying degrees as well as ether group participation in the brown seaweeds and for Cr(VI) binding to the red seaweeds.

Effect of epiphytism on reproductive and vegetative lateral formation in the brown, intertidal seaweedAscophyllum nodosum(Phaeophyceae)

SUMMARYIn the brown algaAscophyllum nodosum(L) Le Jolis, a common species on sheltered Northern temperate rocky shores, gametes are produced in receptacles that emerge from small depressions (lateral pits) along the branched frond. These lateral pits are also the preferred settling site for the obligate epiphytePolysiphonia lanosa(L) Tandy.Therefore, epiphytism can be expected to interfere with host reproductive output. The present study investigated the potential impact of the epiphyte onA. nodosumin two series of laboratory experiments that measured: (i) the direct shading of the host plant underneath an epiphyte canopy; and (ii) the development of receptacles in clean and epiphytisedA. nodosumsegments (excised from individual fronds) over a 6 month period. These experiments showed that light reaching emerged fronds underneath a dense epiphyte cover was reduced by 40%, and this was independent of the degree of desiccation the epiphyte experienced. Concurrently, in the growth study with epiphytisedA. nodosumsegments (segments with one clean and one epiphytised lateral pit) total receptacle biomass per epiphytised fragment was significantly reduced compared with clean segments (0.52 g and 1.25 g per gram of frond segment, respectively), although this effect was only significant inA. nodosumfrom sheltered shores. However, expressed as biomass per lateral pit, receptacle biomass in the remaining clean lateral pits in epiphytised segments was significantly increased in segments from both shores, demonstrating thatA. nodosumcan at least partially compensate for the loss of production resulting from epiphytism.

Cu(II) binding by dried biomass of red, green and brown macroalgae

Dried biomass of the marine macroalgae Fucus spiralis and Fucus vesiculosus (brown), Ulva spp. (comprising Ulva linza, Ulva compressa and Ulva intestinalis) and Ulva lactuca (green), Palmaria palmata and Polysiphonia lanosa (red) were studied in terms of their Cu(II) biosorption performance. This is the first study of its kind to compare Cu(II) uptake by these seaweeds in the South-East of Ireland. Potentiometric and conductimetric titrations revealed a variety of functionalities on the seaweed surface including carboxyl and amino groups, which are capable of metal binding. It was also found that, of the seaweeds investigated, F. vesiculosus contained the greatest number of acidic surface binding sites while Palmaria palmata contained the least. The metal uptake capacities of the seaweeds increased with increasing pH and kinetic behaviour followed a similar pattern for all seaweeds: a rapid initial sorption period followed by a longer equilibrium period. P. palmata reached equilibrium within 10 min of exposure while F. vesiculosus required 60 min. Correlation was found between the total number of acidic binding sites and the time taken to reach equilibrium. Fourier transform infra-red (FTIR) analysis of the seaweeds revealed the interaction of carboxyl, amino, sulphonate and hydroxyl groups on the seaweed surface with Cu 2+ ions while time course studies established the relative contribution of each of these groups in metal binding.

Seasonal Variation in Bromophenol Content of Polysiphonia lanosa

The bromophenol content of Polysiphonia lanosa, determined by GLC-MS, was shown to vary considerably between late spring and early autumn. The lowest content was found in material collected in early May and then the levels rose until a peak was reached in July. When the extracts were tested for cytotoxicity against DLD-1 cells, a direct correlation was shown between cytotoxicity and bromophenol abundance, confirming that these compounds are the ones responsible for the cytotoxicity of the species.

Composition and spatio temporal variability of the epiphytic macroalgal assemblage of Fucus vesiculosus Linnaeus at Clare Island, Mayo, western Ireland

The composition and the patterns of spatial and temporal variability of the epiphytic assemblages of Fucus vesiculosus of Clare Island, on the western coast of Ireland, were investigated for an annual cycle. Specimens of Fucus were collected on seven sampling dates from three sites of the island (Portlea, Kinnacorra and Portnakilly). Data of cover of the most common epiphytic species were collected and analysed by multivariate and univariate techniques. Elachista fucicola, Polysiphonia lanosa, Porphyra umbilicalis, Spongonema tomentosum and Ulva compressa were the most common species. Spatial and temporal variation was detected both for the whole assemblage and for the most abundant species. In general, the assemblage was quantitatively more abundant and diverse in spring–summer than in autumn–winter. In spring–summer, there was a clear differentiation among the assemblage of Portnakilly and the assemblages of the other two sites. Individual species were also generally more abundant in spring–summer and their distribution at the three sites was often not consistent in time; P. lanosa was the only epiphyte for which a consistent effect of site was found. Spatial variation on a scale of meters to tens of meters was the most striking pattern of distribution of the epiphytic assemblage; significant effects related to this spatial scale were detected both for the whole assemblage and for individual species. Phenological patterns of the epiphytic species determining availability of propagules and limited dispersal, leading to aggregated patterns of distribution, are considered the main factors responsible of such patchiness. The importance of the incorporation of small spatial scales in sampling designs analysing the distributional patterns of epiphytic assemblages is discussed.

In-vitro cytotoxic activities of the major bromophenols of the red alga Polysiphonia lanosa and some novel synthetic isomers.

Bioassay-guided fractionation was applied to the cytotoxic chloroform fraction of the red alga Polysiphonia lanosa. The major compounds of the most active fraction were identified using GLC-MS analysis as lanosol (1), methyl, ethyl, and n-propyl ethers of lanosol (1a, 1b, and 1c, respectively), and aldehyde of lanosol (2), although 1b appears to be an artifact arising during the fractionation procedure. These compounds and other known bromophenols were synthesized in addition to four novel isomers (3, 3a-c). The cytotoxic activities of all the synthetic compounds were determined against DLD-1 cells using the MTT assay. Compounds with IC(50) < 20 micromol were also tested against HCT-116 cells. Compound 3c (2,5-dibromo-3,4-dihydroxybenzyl n-propyl ether) was the most active compound against both cell lines (IC(50) = 1.72 and 0.80 micromol, respectively), and its effect on the cell cycle was studied using flow cytometry.

Carbon exchange between Polysiphonia lanosa (Rhodophyceae) and its brown algal host

Polysiphonia lanosa and its preferred Ascophyllum nodosum host exchange 14C-labeled photoassimilates. Exchange was demonstrated by injecting 14C-bicarbonate into air bladders on 15-30 cm cultured sections of field-collected host blades. Each section bore rhizoidally attached Polysiphonia. In a separate set of experiments, Polysiphonia on similar host material was surface treated with 14C-bicarbonate in sealed vessels. Movement of radioactive label was detected by autoradiographic and liquid scintillation techniques. On average, 10.5% of total label moved from host to hemiparasite following the first treatment, and 9.7% moved from hemiparasite to host following the second. Reciprocal exchange of tagged photoassimilates may play an important role in the specificity of the relationship between these two algal species.

Reproductive biology of the red alga Polysiphonia lanosa (Ceramiales) in the Bay of Fundy, Canada

The purpose of this investigation was to establish reproductive phenology of the dioecious marine floridean red alga Polysiphonia lanosa (L.) Tandy. Specifically, the distribution and frequencies of male and female plants, timing of their sexual maturity, fecundity and success of fertilization were investigated. The presence of cystocarps was taken as an indication of syngamy. Populations of P. lanosa in the Bay of Fundy reproduce in spring, summer and autumn. Both male and female filaments were present in equal abundance at all sampling locations, grew in close proximity, and occurred with equal abundance at all elevations above chart datum. During the growing season most of the mature plants contained reproductive organs with apparently functional gametangia containing gametes the structure and behavior of which conformed to those reported in the literature for other species of the genus. Male and female plants of P. lanosa matured synchronously during late May to early July at all collecting sites. The ratio of spermatia to carpogonia calculated for the sampled population was high, 3000–4800 spermatia:1 carpogonium. At the end of the growing season (late October) the fertilization success was at its maximum of 50 to 90% and at its minimum in July at 24%. The three free-living life-history phases (females, males and tetrasporophytes) were abundant and occurred with equal frequency, indicating that a complete life cycle was common at the studied location.

The meiofauna of Ascophyllum nodosum (L.) Le Jolis: characterization of the assemblages associated with two common epiphytes

The meiofaunal assemblages associated with 2 common epiphytes of Ascophyllum nodosum (L.) Le Jolis, Pilayella littoralis (L.) Kjellman and Polysiphonia lanosa (L.) Tandy on a sheltered rocky shore in North Wales are described. A total of 40 permanent meiofaunal species was found, of which 26 were harpacticoid copepods. Faunal abundance in both epiphytes displayed little temporal variation at high taxonomic levels, but classification analysis detected differences in species composition that were sufficient to highlight seasonal changes and to discriminate between epiphytes. Diversity was generally higher in Polysiphonia assemblages and this was attributed to the greater habitat complexity provided by this particular species.

Settlement of larvae of the giant scallop, Placopecten magellanicus, in 9-m deep mesocosms as a function of temperature stratification, depth, food, and substratum

In January and February 1992 an experiment was conducted in a 10.5-m deep tank (diameter: 3.7 m, volume: 117 m3) to examine the effects of food distribution with respect to a stable thermocline, depth, and substratum type on the settlement and metamorphosis of larvae of the giant scallop, Placopecten magellanicus (Gmelin). Polyethylene tube bags (diameter: 0.60 m) were used to enclose 9-m deep columns of seawater which were then used as treatment replicates. A sharp thermocline (i.e. 7 to 11°C gradient) was created between a depth of 4.0 and 5.0 m. At the beginning of the experiment, one million 6-d old larvae were added to the surface of each tube. Two or three replicate tubes of each of four feeding treatments were established: (1) food (Isochrysis galbana) added to the top 1 m of the water column (“top-fed”, n=3); (2) food added to the bottom 1 m of the water column (“bottom-fed”, n=3); (3) food added throughout the water column (“mixed”, n=3); and (4) no food added (“unfed”, n=2). Settlement collectors were placed in two replicate tubes of each treatment at depths of 0.1, 4, 5, and 9 m and contained two different substrata, Polysiphonia lanosa (a red filamentous alga) and aquarium filter-wool as an algal mimic. Spat settlement in the different feeding treatments was a function of larval growth rate. Most spat were collected in the mixed tubes. Fewer individuals were collected in the top-fed treatment and fewer still in the bottom-fed treatment; minimal numbers of spat were found in the unfed tubes. Filter-wool collected more spat than P. lanosa, but this was evident only in the 4-m deep collectors in the mixed tubes. Most spat were found in the 0.1-m or 4-m deep collectors; generally few were located below the thermocline in collectors at 5 or 9 m. We suggest that, in areas of intense stable stratification, spat collection of the giant scallop may be enhanced by the placement of collectors with appropriate substratum material at or above the zone of stratification, rather than near the bottom. Furthermore, we propose that natural settlement may be increased in areas where a stratification layer intersects with the sea floor or where the layer is disrupted by turbulent mixing.